1. Field of the Invention
The present invention relates to a process for preparing a cation-exchange membrane which has excellent electrical characteristics and cation selective permeability, chemical resistance, heat resistance and mechanical strength. More particularly, it relates to a process for preparing a cation-exchange membrane which is suitable as a diaphragm for electrolysis of an alkali metal halide.
2. Description of the Prior Art
Cation-exchange membranes have been used in various industries because of their excellent electrical characteristics and cation selective permeability.
Various cation-exchange membranes have been proposed since the electrolysis processes using an ion-exchange membrane have been developed. However, a cation-exchange membrane having satisfactory cation selective permeability, chemical resistance and electric characteristics has not been found.
The conventional cation-exchange membranes have high resistance to the permeation of most anions; however, they have disadvantages such as remarkably high mobility of anions when the electrolyte is an aqueous solution containing hydroxyl ions in comparison with other cases.
The phenomenon is observed because the permeation of hydroxyl ions can not be effectively prevented since the mobility of hydroxyl ions in an aqueous solution is remarkably high in comparison with the other anions.
When the cation-exchange membrane is used with solutions containing hydroxyl ions, for example as a diaphragm for electrolysis of sodium chloride, the current efficiency is lowered disadvantageously because of the phenomenon.
Accordingly, it has been required to develop a cation-exchange membrane having high durability and high resistance to permeation of hydroxyl ions in these usages of the cation-exchange membrane.
The inventors have studied to develop a cation-exchange membrane for satisfying the requirements of durability and permeation of hydroxyl ions.